Effects of pre‐freezing methods and storage temperatures on the qualities of crucian carp ( Carassius auratus var. pengze) during frozen storage

Pengze crucian carp was pre-frozen by liquid nitrogen and freezer, and then stored at −20/−40°C and −20°C, respectively, for 15–60 days. Effects of pre-freezing methods and storage temperatures on the qualities of fish were investigated. The pH showed a "V" trend. The soluble myofibrillar protein content, hardness, springiness, cohesiveness, gumminess, chewiness, and resilience decreased. Thiobarbituric acid value, total volatile basic-nitrogen value, thawing and cooking loss rates increased with the extending of storage period. LF-NMR analysis indicated that the water-protein connection became less tight. Moreover the qualities decline degrees were higher for freezer pre-frozen than liquid nitrogen pre-frozen, and higher for −20°C storage than −40°C storage. Accordingly, compared with conventional freezer pre-freezing and storage, liquid nitrogen pre-freezing and low temperature storage could inhibit the oxidation and degradation, and keep better water holding and textural properties of muscle. The present study showed a great potential application in aquatic products processing industry. Practical applications In aquatic product enterprise, liquid nitrogen can be used to pre-freeze fishes in seconds. And combined with low temperature storage, the oxidation and degradation of fish can be significantly inhibited. In addition, water holding capacity and textural properties of fish muscle can be better kept, and the shelf-life of fish can be extended by several weekends in comparison with those of fishes pre-frozen and stored in freezer.